The invention relates generally to a structure for an arrangement of mechanical gears, and more particularly to such a structure for supporting toothed gears in an aircraft.
Known housings for arrangements of mechanical gears carried on supporting axles or shafts, which are arranged in fixed spatial relationship with each other, normally take the form of substantially closed containers of grey iron or light metal corresponding to the geometric arrangement of the bearings for journaling the axles or shafts of the gears. Such known housings have been provided with stiffening ribs on the inside and/or the outside thereof for the transmission and distribution of the reaction forces acting on the bearings. Such reaction forces can be extremely high because of the high reduction ratios and developing torque of the gear arrangements, particularly when used in aircraft, and can result in localized mixed stresses in the supporting wall areas of the housing because of stress overlap.
In modern type gear arrangements, particularly those known as Novikov gear arrangements, which permit high reduction ratios in highly stressed gearing steps, and which have gear wheels of light weight, the housing must be very stiff and not deform when under load in order to avoid any impairment of the geometric conditions to permit proper gear engagement and to thus avoid any impairment of the load capacity of the gear arrangement. While it might be possible to achieve this objective using housings of the known type, it would require very large wall thicknesses resulting in high material costs and excessive weight, which is particularly undesirable in aircraft. Even if the known housing were to be made of fiber reinforced materials, large wall thicknesses and corresponding high material costs and weight would still result since the known type of housing structure must be formed of a plurality of superimposed layers having different fiber direction because of the anisotropic strength and stiffness properties of such fiber compound materials. Accordingly, the plurality of superimposed layers would still result in increased wall thicknesses and increased weight. Additionally, the known type of housings for gearing arrangements have been difficult to manufacture because of their generally complicated shapes.
It is accordingly the general object of the invention to provide a housing for an arrangement of mechanical gears, particularly of the heavy duty type, which is light in weight yet provides substantially deformation free support of gearing steps even when the gearing steps are highly stressed and have high transmission ratios.